1. Field of the Invention
Example embodiments relate to a method of testing semiconductor memory devices. More particularly, example embodiments relate to a method for determining whether a probe provides a weak contact with a pad of a semiconductor memory device, and a semiconductor memory device using the same
2. Description of the Related Art
Generally, in order to test a semiconductor memory device, an electric signal may be applied to pads of the semiconductor memory device to determine whether data output from the semiconductor memory device is normal. Accordingly, a device, e.g., a probe, may come into contact with the respective pads so that the electric signal may be applied to the pads. However, as capacity of the semiconductor memory device increases, the number of pads receiving and outputting electric signals also increases. Thus, in order to reduce the testing time, the probes may come into contact with the pads simultaneously. However, because the number of pads simultaneously coming into contact with the probes increases, it may be difficult to correctly align the probes to with the respective pads.
Further, testing may be conducted numerous times and, thus, it may also be difficult to repeatedly bring the probes into correct contact with the respective pads, e.g., if a probe comes into contact with an edge of the pad, a problem may occur.
FIG. 1 illustrates pads of a related art semiconductor memory device and probes for testing the related art semiconductor memory device. Referring to FIG. 1, the related art semiconductor memory device may include a sensor pad 110 and pads 115_1 and 115_2 in order to perform a test. The pads 115_1 and 115_2 may be used to input/output an electric signal to/from the semiconductor memory device, and the sensor pad 110 may be used to determine whether probes 155_1 and 155_2 correctly come into contact with the pads 115_1 and 115_2.
The sensor pad 110 may include a probe region 111 and a sensing region 112. The probe region 111 may normally come into contact with a probe 150. The sensing region 112 may surround the probe region 111, and may determine whether a probe 150 is out of the probe region 111. The probe region 111 may be formed of an insulating material, and the sensing region 112 may be formed of a conductive material.
The related art semiconductor memory device may be tested by applying a current to the probe 150 coming into contact with the sensor pad 110, and measuring a voltage of the sensor pad 110, e.g., the current may not flow through the sensor pad 110 when the probe 150 normally comes into contact with the probe region 111, or the current may flow through the sensor pad 110 when the probe 150 abnormally comes into contact with the sensing region 112. Accordingly, the voltage measured from the sensor pad 110 may depend on whether the probe 150 normally (or abnormally) comes into contact with the probe regions 111, 112. However, an additional channel CH1 may be required for the sensor pad 110, e.g., the channel CH1 for measuring the current or voltage of the sensor pad 110 must be added to channels CH2 and CH3 used to measure the currents or voltages of pads 115_1 and 115_2.
Another possible test method is to apply a current or a voltage to the probe 150 and measure the voltage or current of one of the normal pads 115_1 and 115_2. However, although an additional channel, e.g., channel CH1, may not be needed, it may be impossible to determine whether the probe 150 correctly comes into contact with the sensor pad 110 when an impeding substance, e.g., dust, exists on the sensor pad 110. In particular, even when the probe 150 normally comes into contact with the probe region 111, a voltage or current may be measured from pads 115_1 and 115_2 due to conductivity of the impeding substance (e.g., dust) on the probe region 111 of the sensor pad 110. Accordingly, the normal contact of the probe 150 with the sensor pad 110 may be sensed as having an abnormal contact because impeding substances on the probe region 111 may exist.